Conventional switching devices for gas discharge tube displays, such as those using neon tubes, are either mechanical or electronic devices that control the primary (low-voltage) side of the transformers. A significant problem with this approach, among other problems, is that it requires a transformer for each tube. Multiple such transformers multiply the complexity, cost and weight of the display.
Some mechanical type devices have been used to switch tubes on the secondary side of the transformer. However, among other problems, this approach produces significant R.F.I. (radio frequency interference) and/or E.M.I. (Electro-magnetic interference).